The mitotic and meiotic chromosome ofPericoma modestawere analyzed. Diploid complement was 2n= 14 and includes the sex-chromosomes which have never been observed in other species of Psychodidae. The heterosomes did not undergo synapsis to form a bivalent at the meiosis, but regularly passed to opposite poles at the first anaphase. This characteristic makes this species comparable to some tipulid flies.